Drug delivery devices of similar appearance may be provided for delivering different types of drugs. In particular, a single user may use devices comprising a similar exterior shape for dispensing different drugs. It is desirable that mixing-up different devices and, hence, different drugs is prevented.
A drug delivery device is described in document EP 1 923 083 A1, for example.
Cartridges are generally marked with details of the medicament that they contain, and may be differentiated with a specific color for that medicament. Although the cartridge itself is marked with details of the medicament that it contains, this marking may be difficult to see after the cartridge is loaded into the device, so the user may select the wrong device, and dispense the wrong medicament. It would therefore be advantageous for a reusable drug delivery device to be marked with a medicament differentiation. However, with a differentiated reusable device there is a risk that the user might load a cartridge in the wrong device, and then rely on the differentiation on the device rather than reading the cartridge label, and so dispense the wrong medicament. Alternatively, all detachable parts of the reusable device might be dedicated (or mechanically coded) to each other, but without any differentiation. For example, the cartridge might be coded to the cartridge holder, the cartridge holder to the dose setting mechanism, and the cap to the dose setting mechanism. The risk of a fully dedicated device is that it might be difficult to understand, so the user might apply excessive force to assemble the device, and damage the coding so that a cartridge fits into an incorrect device.